Method for controlling the operating response of a hybrid drive of a vehicle

ABSTRACT

A method of controlling the operating response of a hybrid drive of a vehicle is described, the hybrid drive having an internal combustion engine and at least one electric motor as the drive motors, and the drive shafts of the drive motors being mechanically linkable to a drive train of the vehicle.  
     A drag torque characteristic curve ( 52 ) for the hybrid drive ( 14 ) is established by targeted activation of the at least one electric motor ( 20, 22 ).

[0001] The present invention relates to a method for controlling theoperating response of a hybrid drive of a vehicle, the hybrid driveincluding an internal combustion engine and at least one electric motoras the drive motors, and the drive shafts of the drive motors beingfunctionally connectable to a drive train of the vehicle.

BACKGROUND INFORMATION

[0002] Hybrid drives for vehicles are known. In the hybrid drivesclaimed here, an internal combustion engine is combined with at leastone electric motor so that multiple drive sources are provided for thevehicle. According to the requests specified by a vehicle driver, thedrive sources can optionally supply their drive moments to a drive trainof the vehicle. Depending on the actual driving situation, this resultsin various drive configuration possibilities for the drive, in a mannerknown as such, which in particular are used for improving drivingcomfort and reducing energy use as well as pollutant emissions.

[0003] In hybrid drives for vehicles, serial configurations, parallelconfigurations, and mixed configurations of an internal combustionengine and electric motors are known. Depending on the configuration,the electric motors may be directly or indirectly coupled to the drivetrain of the internal combustion engine. For the mechanical linkage ofthe internal combustion engine and/or the electric motors, it is knownto provide these with a mechanically linkable configuration via gearing,for example planetary gears or the like, and clutches.

[0004] It is known that the internal combustion engine functions as themain drive source for the vehicle, while the electric motors, dependingon the actual driving situation, may be engaged or disengaged. In drivedesigns it is known that for a negative torque request by a vehicledriver the internal combustion engine delivers a drag torque which isdetermined by the internal losses in the internal combustion engine as afunction of an instantaneous engine rotational speed. If the gears arechanged during the negative torque requests by the vehicle driver, forexample in the operation of a manual transmission or actuation of ahydrodynamic converter (automatic transmission), abrupt variations inthe output torque of the drive result on account of the abrupt change inthe rotational speed acting on the drive train (corresponding to thegear position selected). This is caused by the fact that the drag torqueof the internal combustion engine is a function of the rotational speed.

ADVANTAGES OF THE INVENTION

[0005] The method according to the present invention having the featuresstated in claim 1, in contrast, offers the advantage that the dragtorque is independent of the engine rotational speed of the internalcombustion engine when the vehicle driver requests a negative torque(drag torque). By establishing a drag torque characteristic curve forthe hybrid drive through a targeted activation of the at least oneelectric motor of the hybrid drive, it is advantageously possible toinfluence in a targeted manner a drag torque characteristic curve of thehybrid drive as a function of the vehicle speed. By activating the atleast one electric motor, the drag torque of the internal combustionengine may be compensated for in whole or in part, or an additional dragtorque may be generated by operating the electric motor in generatormode.

[0006] In particular, by disengaging the internal combustion engine fromthe drive train, by engaging the clutch, for example, drag torques maybe applied solely by the at least one electric motor, therebyestablishing a drag torque response for the vehicle to which the vehicledriver is accustomed. In each case, an abrupt response of the dragtorque characteristic curve of the internal combustion engine, and thusof the hybrid drive, may be compensated for by the resulting variationsin the activation of the electric motor.

[0007] In one preferred embodiment of the present invention, a so-calledcoasing operation of the hybrid drive is achieved without disengagingthe internal combustion engine from the drive train. The drag torqueapplied by the internal combustion engine is compensated for byactivating the at least one electric motor in such a way that the dragtorque of the internal combustion engine is exactly compensated for by apositive torque of the at least one electric motor. The vehicle is thendecelerated solely by the drive resistance acting on the vehicle.

[0008] In addition, in one preferred embodiment of the present inventionit is possible to vary the drag torque characteristic curve as afunction of a braking request of a vehicle driver by the targetedactivation of the at least one electric motor. This enables brakingsupport to be easily provided by increasing a drag torque of the hybriddrive.

[0009] Additional preferred embodiments of the present invention resultfrom the other features stated in the subclaims.

DRAWINGS

[0010] The present invention is explained in greater detail below withreference to the associated drawing.

[0011]FIG. 1 shows a torque characteristic curve of an internalcombustion engine;

[0012]FIG. 2 shows the variation of an output torque of a vehicle;

[0013]FIG. 3 schematically shows a hybrid drive of a vehicle;

[0014]FIG. 4 shows a block diagram of the influence on the drag torqueof the hybrid drive;

[0015]FIG. 5 shows the drag torque characteristic curve of drive sourcesfor the hybrid drive;

[0016]FIG. 6 shows various drag torque characteristic curves of thehybrid drive; and

[0017]FIG. 7 shows a block diagram of the coordination of drag torqueinfluencing as a function of a braking request for the vehicle.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0018]FIG. 1 shows for illustrative purposes a torque characteristiccurve of an internal combustion engine as a function of the rotationalspeed. A maximum torque characteristic curve 10 for a power request by avehicle driver is illustrated, as well as a drag torque characteristiccurve 12 for a negative power request by the vehicle driver. A negativepower request is present when the vehicle driver does not actuate thegas pedal of the vehicle; i.e., the gas pedal is at or approximately atthe zero position. Based on characteristic curve 12 in FIG. 1, it isapparent that in this operating mode of the vehicle, drag torquecharacteristic curve 12 is established as a function of enginerotational speed n. The higher the engine rotational speed n, the higherthe drag torque. The drag torque is negative with respect to the outputtorque of the internal combustion engine, and in particular is afunction of internal losses in the internal combustion engine, inparticular friction and the like. Above drag torque characteristic curve12 a region 15 is designated which cannot be adjusted by activating theinternal combustion engine, for example, for non-Diesel internalcombustion engines, a region which cannot be adjusted by positioning athrottle valve or specifying an ignition angle, and for Diesel engines,a region which cannot be adjusted by a fuel injection quantity. It isclear that an operating point of the internal combustion engine isdefined by engine rotational speed n and torque M, the upper limit beingbounded by maximum torque characteristic curve 10 and the lower limitbeing bounded by drag torque characteristic curve 12.

[0019]FIG. 2 illustrates an output torque M_(A) as a function of time t.It is assumed here that at a time t₁ a transmission mechanically linkedto the internal combustion engine is switched, for example by manual orautomatic shifting, resulting in an abrupt change in output torque M_(A)when a negative torque on the internal combustion engine is requested bya vehicle driver. This abrupt change in output torque M_(A) acts on thedrive wheels of the vehicle and results in impaired driving comfort.

[0020]FIG. 3 schematically illustrates a hybrid drive 14 of a vehiclewhich includes an internal combustion engine 16 having thecharacteristic curves illustrated in FIGS. 1 and 2. FIG. 3 illustrates aparallel hybrid drive in which a drive train 18 includes at least one,in this case two, electric motors 20 and 22 in addition to internalcombustion engine 16. Drive train 18 includes clutches 24, 26, and 28and transmission 30. By engaging clutches 24, 26, and/or 28 andactivating internal combustion engine 16 or electric motor 20 and/or 22,it is possible to establish a selectable output torque on drive shaft 32of drive train 18. The structure and operating principle of suchparallel hybrid drives 14 are generally known, so that further detail isnot provided within the scope of the present description.

[0021]FIG. 4 shows once more, in a block diagram, the possibility ofinfluencing the drag torque of the configuration shown in FIG. 3. It isassumed that a negative torque request by a vehicle driver is present;i.e., the gas pedal is at or approximately at the zero position. Thisnegative torque request 34 is fed to a drag torque coordinator 36. Dragtorque coordinator 36 may be formed from a circuit system, not shown indetail, which for example is a component of a control unit (motorcontrol unit) of hybrid drive 14. Drag torque coordinator 36 sendscontrol signals 38, 40, and 42. Control signals 38, 40, and 42 activateinternal combustion engine 16 or electric motors 20 and 22 in such a waythat these signals request a defined torque M₁₆, M₂₀, or M₂₂ which acton drive train 18. In the example shown, two electric motors 20 and 22are assumed, it being clear that the number of electric motors may begreater or smaller, so that a corresponding number of control signalsfor electric motors 20 and 22 is provided by drag torque coordinator 36.A control signal 44 is also fed to drag torque coordinator 36 whichcorresponds to the instantaneous gear ratio of transmission 30, and thusto its gear position.

[0022]FIG. 5a illustrates once again drag torque characteristic curve 12for internal combustion engine 16, clearly showing the dependency of thecharacteristic curve on rotational speed n. FIG. 5b shows the maximumand minimum possible torque characteristic curves 46 and 48,respectively, of an electric motor as a function of rotational speedn_(E) of the electric motor. Rotational speed n_(E) of the electricmotor is a function of the supply voltage, for example, so thatrotational speed n_(E) of electric motors 20 and 22, and thus theirtorque M_(E), may be readily controlled by signals 40 and 42 (FIG. 4).

[0023] Based on FIGS. 5a and 5 b, it is apparent that it is possible toestablish a resulting drag torque characteristic curve for hybrid drive14 by superimposing the torque characteristic curve of internalcombustion engines 16 and the torque characteristic curves of electricmotors 20 and 22. When clutches 24, 26, and 28 are engaged, the sum ofsuperimposed torques M_(V) or M_(E) is the maximum achievable dragtorque of hybrid drive 14. The dependency of the torques on rotationalspeed n_(V) or n_(E) results in a dependency on instantaneous vehiclespeed v.

[0024]FIG. 6 clarifies once again a superimposition of drag torquecharacteristic curve 12 for internal combustion engine 16 on therespective maximum or minimum torque characteristic curves 46, 46′ and48, 48′ of electric motors 20 or 22, respectively. In each case thetorques are plotted as a function of vehicle speed v. Drag torquecharacteristic curve 12 is plotted as a characteristic curve family(dash-dot-dash-line), the various drag torque characteristic curves 12resulting from the instantaneous engaged mode of transmission 30. Fivedrag torque characteristic curves 12 are plotted in FIG. 6, assuming a5-speed manual transmission 30. The maximum torque characteristic curvesof electric motors 20 and 22 are represented by 46 and 46′,respectively, and the minimum torque characteristic curves of electricmotors 20 and 22 are represented by 48 and 48′, respectively.

[0025] Corresponding to the engagement of clutches 24, 26, and 28,various possibilities are selected for influencing the overall dragtorque of hybrid drive 14 by internal combustion engine 16 or electricmotors 20 and 22. The following possibilities result, for example:

[0026] 1. Clutch 28 is disengaged, so that the drag torque is determinedsolely by electric motor 22.

[0027] 2. Clutches 28 and 26 are engaged and clutch 24 is disengaged, sothat the drag torque of hybrid drive 14 is determined by electric motors20 and 22.

[0028] 3. Clutches 24, 26, and 28 are each engaged, so that the dragtorque of the hybrid drive is determined by electric motors 20 and 22 aswell as by internal combustion engine 16.

[0029] It is clear that various superimpositions of drag torquecharacteristic curve 12 of internal combustion engine 16 are possible asa function of the activations of clutches 24, 26, and 28 and of electricmotors 20 and 22. When clutch 24 is disengaged, a so-called coasingoperation of hybrid drive 14 is initiated, in this case it still beingpossible to influence the drag torque by electric motors 20 and 22.

[0030] In FIG. 6, the maximum possible drag torque characteristic curveof hybrid drive 14 is denoted by reference number 50. This results whendrag torque characteristic curve 12 of the internal combustion engine issuperimposed on minimum torque characteristic curves 48 and 48′ ofelectric motors 20 and 22. As shown in FIG. 6, this maximum possibledrag torque characteristic curve 50 exhibits discontinuities as afunction of vehicle speed v. For this reason a continuous drag torquecharacteristic curve 52 is selected by drag torque coordinator 36, whichis maximally matched to maximum possible drag torque characteristiccurve 50. This selected drag torque characteristic curve 52 is obtainedby storing control signals 38, 40, and 42 for internal combustion engine16 or electric motors 20 and 22 in drag torque coordinator 52 for eachvehicle speed v as a function of the gear position of transmission 30(signal 44). Electric motors 20 and 22 may be operated in engine mode orgenerator mode within their maximum or minimum characteristic curves 46,48, respectively, so that it is possible to set drag torquecharacteristic curve 52 for hybrid drive 14 by the resultingsuperimposition of characteristic curves.

[0031] Of course, other drag torque characteristic curves 52 may beselected by executing appropriate routines. Drag torque coordinator 36may optionally be provided with a characteristic map control whichenables various drag torques to be set as a function of additionaloperating parameters of the vehicle for the same vehicle speeds v.

[0032] A flow diagram for variation of drag torque characteristic curve52 as a function of an actuation of the vehicle brakes is illustrated asan example in FIG. 7. Initially there is no request for a negativetorque (no drag torque by the vehicle driver) according to field 60. Aquery 62 continually checks whether a drag torque request is present.This can be achieved by monitoring the position of the gas pedal, forexample. If the position of the gas pedal is below a specifiable limit,drag torque coordinator 36 is activated by signal 34 (negative torquerequest). If the position of the gas pedal is not below the specifiablelimit, the request remains “no drag torque” (field 60).

[0033] Drag torque coordinator 36 generates signals 38, 40, and 42,resulting in the establishment of drag torque characteristic curve 52.As shown in FIG. 6, this drag torque characteristic curve 52 is definedas a function of speed.

[0034] If the braking device is actuated during the drag torque requestby the vehicle driver, so that detection may be performed, for examplethrough a signal applied to a brake light switch, when the brakingdevice is actuated a query 64 sends a signal to drag torque coordinator36, which then increases the drag torque one time (field 52+). If thevehicle driver actuates the brake again (query 66), a new control signalis generated at drag torque coordinator 36 which then further increasesthe drag torque, either to a higher level or up to the maximum dragtorque (field 52++). A query 68 constantly monitors whether a furtherpositive torque request by the vehicle driver, for example by actuationof the gas pedal, is made. If this positive torque request is made,control of the drag torque characteristic curve is transferred in field60 so that the drag torque is reduced by a transition function, andhybrid drive 14 is controlled corresponding to the positive torquerequest.

[0035] The explanations make it clear that many different drag torquecharacteristic curves for hybrid drive 14 may be established by dragtorque coordinator 36. This may be achieved as a function of vehiclespeed v and/or as a function of an actuation of the vehicle brakes. Asdiscussed, this may involve two or more steps. Gas pedal dynamics, forexample, may be taken into account as an additional control variable.The gas pedal dynamics may be derived from a gradient of a gas pedalsignal, for example. Additional influencing variables may be, forexample, a given roadway grade such as when traveling downhill or thelike. In this case the drag torque may be adjusted in such a way that aconstant speed v of the vehicle is maintained.

[0036] In summary, it is apparent that a negative torque for theoperating points of hybrid drive 14 may be specified, within thephysical limits of hybrid drive 14, by influencing the drag torquecharacteristic curve via drag torque coordinator 36. In particular, dragtorque characteristic curves may be established which are independent ofthe rotational speed. In addition, sudden changes in torque duringdownshifting of transmission 30 are prevented by regulation ofspeed-dependent drag torque curves. Furthermore, the drag torqueresponse of hybrid drive 14 may be taken into account during changes ofthe operating mode, for example internal combustion engine mode,electric motor mode, or combined internal combustion engine and electricmotor mode. Lastly, a so-called coasing operation is also possible wheninternal combustion engine 16 is engaged in drive train 18 by electricmotors 20 and/or 22 compensating for the drag torque of internalcombustion engine 16.

[0037] The explanation of the exemplary embodiment was based on aparallel hybrid drive 14. Of course, the operating response of thehybrid drive may be controlled by influencing a drag torquecharacteristic curve for serial hybrid drives and mixed (parallel andserial) hybrid drives as well.

What is claimed is:
 1. A method for controlling the operating responseof a hybrid drive of a vehicle, the hybrid drive comprising an internalcombustion engine and at least one electric motor as the drive motors,and the drive shafts of the drive motors being operatively connectibleto a drive train of the vehicle, wherein a drag torque characteristiccurve (52) for the hybrid drive (14) is established by targetedactivation of the at least one electric motor (20, 22).
 2. The method asrecited in claim 1, wherein drag torques may be applied solely by the atleast one electric motor (20, 22) by disengaging the internal combustionengine (16) from the drive train (18).
 3. The method as recited in oneof the preceding claims, wherein a so-called coasting operation of thehybrid drive (14) is achieved without disengaging the internalcombustion engine (16) from the drive train (18).
 4. The method asrecited in one of the preceding claims, wherein the continuous dragtorque characteristic curve (52) is maximally matched to a maximumpossible drag torque characteristic curve (50).
 5. The method as recitedin one of the preceding claims, wherein the drag torque characteristiccurve (52) is determined by a drag torque coordinator (36) whichprovides control signals (38, 40, 42) for the drive motors (16, 20, 22)from a negative torque request (34) and a gear position (signal 44). 6.The method as recited in claim 5, wherein the control signals (38, 40,42) are provided as a function of an instantaneous speed (v) of thevehicle.
 7. The method as recited in one of the preceding claims,wherein electric motors (20 and 22) are operated in generator modeand/or engine mode for influencing the drag torque characteristic curve(52).
 8. The method as recited in one of the preceding claims, whereinthe drag torque request is picked up by monitoring the position of thegas pedal of the vehicle.
 9. The method as recited in one of thepreceding claims, wherein the drag torque characteristic curve (52) isinfluenced as a function of additional operating parameters of thevehicle.
 10. The method as recited in claim 9, wherein the drag torquecharacteristic curve (52) is varied as a function of a braking requestby a vehicle driver by targeted activation of the at least one electricmotor (20, 22).
 11. The method as recited in claim 10, wherein the dragtorque is increased in a stepwise manner.